Associated production of a top pair and a W boson at next-to-next-to-leading logarithmic accuracy
Associated production of a top pair and a
Alessandro Broggio 0 1 3 6 7 8
Andrea Ferroglia 0 1 3 4 5 7 8
Giovanni Ossola 0 1 3 4 5 7 8
Ben D. Pecjak 0 1 2 3 7 8
0 365 Fifth Avenue , New York, NY 10016 , U.S.A
1 300 Jay Street, Brooklyn, NY 11201 , U.S.A
2 Institute for Particle Physics Phenomenology, Ogden Centre for Fundamental Physics
3 James Franck-Stra e 1 , D-85748 Garching , Germany
4 Physics Department, New York City College of Technology, The City University of New York , USA
5 The Graduate School and University Center, The City University of New York , USA
6 Physik Department T31, Technische Universitat Munchen
7 Science Laboratories , South Rd, Durham DH1 3LE , United Kingdom
8 Department of Physics, University of Durham
We consider soft gluon emission corrections to the production of a top-antitop pair in association with a W boson at the Large Hadron Collider. We obtain a soft-gluon resummation formula for this production process which is valid up to next-to-next-to-leading logarithmic accuracy. We evaluate the soft gluon resummation formula in Mellin space by means of an in-house parton level Monte Carlo code which allows us to obtain predictions for the total cross section as well as for several di erential distributions. We study the impact of the soft-gluon resummation corrections in comparison to xed order calculations.
NLO Computations; QCD Phenomenology
-
boson at
HJEP09(216)8
1 Introduction
2
3
4
5
6
1
Soft-gluon resummation for ttW hadroproduction
Resummation in Mellin moment space
Approximate and resummed formulas
Numerical analysis
5.1
5.2
Total cross section
Di erential distributions
Conclusions
Introduction
cross section of 382+111072 fb [1] while ATLAS measured a total cross section of 369+19010 fb [2].
The two measurements are in perfect agreement with each other but they are about 1:5
larger than the next-to-leading order (NLO) prediction for the cross section [3{7] in the
Standard Model (SM). Furthermore, ATLAS measured a ttW cross section of 0:9
0:3 pb
at 13 TeV [8], in agreement with NLO SM calculations. The associated production of a top
pair and a W or Z boson are the two processes with the heaviest nal states observed to
date at the LHC. These processes are interesting because they provide direct information
about the coupling of the top quark to the carriers of the weak interaction. A variety of
New Physics models predict changes of these couplings with respect to their SM values. In
addition, the associated production of a top pair and a W boson can result in events with
two leptons of the same sign, jets and missing energy. These events, which are relatively
rare in the SM, are exploited in supersymmetry searches.
Recently, some of us applied Soft Collinear E ective Theory (SCET) methods1 in or
der to study the associated production of a top pair and a Higgs boson beyond NLO in
QCD [10]. From the theoretical point of view, the associated production of a top pair and
a W boson is similar to the associated production of a top pair and a Higgs boson and the
associated production of a top pair and a Z boson. In [10], a resummation formula was
obtained and all of the elements appearing in the formula were evaluated to the
perturbative order needed for predictions at next-to-next-to leading logarithmic (NNLL) accuracy.
Among those elements, only the hard function, which receives contributions exclusively
1For a didactic review, see [9].
{ 1 {
from virtual corrections to the tree level partonic processes, is process dependent. The
other ingredients appearing in the resummation formula, namely the soft function and the
evolution matrices, are insensitive to the nature of the color-neutral boson produced in
association to the top pair. The NLO hard functions needed in [10] were obtained by
modifying public codes which allow for the automated evaluation of one-loop virtual correction
to partonic processes, namely OpenLoops [11{17], GoSam [18{22], and MadLoop [23, 24]. The
information encoded in the resummation formula was employed in order to obtain results
that approximate the next-to-next-to-leading order (NNLO) predictions for the ttH cross
section and several di erential distributions depending on the momenta of the
particles. However, a numerical implementation of the resummed soft-gluon emission
corrections, which is computationally more expensive than the evaluation of the approximate
NNLO formulas, was not attempted.
In the present work, we study the resummation of soft gluon emission corrections in
ttW production to NNLL accuracy. The
nal result of our work is a parton level Monte
Carlo code which allows us to evaluate the complete resummation formula and to obtain
predictions for the total cross section and several di erential distributions. This program
will serve as a test study for similar codes which we plan to develop in order to study NNLL
resummation in ttH and ttZ production. In order to build the resummation formula for
the associated (...truncated)